Optical networks use Wavelength Selective Switches (WSS) to dynamically route optical wavelength signals from a source to a destination. WSS devices often rely on wavelength manipulation elements such as liquid crystal on silicon (LCoS) devices or micro-electromechanical (MEMS) mirror arrays to perform the routing.
LCoS devices include a liquid crystal material sandwiched between a transparent glass layer having a transparent electrode, and a silicon substrate divided into a two-dimensional array of individually addressable pixels. Each pixel is individually drivable by a voltage signal to provide a local phase change to an optical signal, thereby providing a two-dimensional array of phase manipulating regions. Manipulation of individual spectral components is possible once an optical signal has been spatially separated by a diffractive element such as a diffraction grating. The spatial separation of spectral components is directed onto predetermined regions of the LCoS device, which can be independently manipulated by driving the corresponding pixels in a predetermined manner.
MEMs devices such as a Digital Micromirror Device (DMD) is comprised of a two-dimensional array of micromirrors or pixels, each actuatable in an ON state or an OFF state. As used herein in the context of a DMD, the terms “micromirror” and “pixel” are used inter-changeably. Typically, a DMD consists of an array of tiny mirrors (typically, several million per square inch), wherein the angular position of each mirror element is individually controllable between at least two positions that are angularly offset from one another by approximately 10 to 20 degrees, for instance. A mirror base is located behind the mirror elements. The individually addressable mirror elements are tiltably mounted on mechanical hinges, and typically the array of mirror elements overlays a layer of controlling circuitry in the mirror base, all of which is mounted on a semiconductor chip. The mirror face of the DMD is composed of a generally rectangular grid array of rectangular or square mirror elements. A typical mirror element is about 16 micrometers square, and the individual elements are separated from one another by a distance of about 1 micron. Individually controlled tilting of the mirror elements in the array around at least one axis allows energy that is reflected from the mirror face to be formed into a predetermined pattern. Further, the mirror face can be substantially instantaneously reconfigured in response to digital signals to form a different pattern. Such reconfiguration is accurate and reproducible, and can generally be achieved in about 25 microseconds or less.
Wavelength selective switches are generally made with either LCoS or MEMs switching technologies. This may limit the performance range of any given switch.